1. Field of the Invention
The present invention generally relates to a resistive random access memory and, more particularly, to a resistive random access memory having different dielectrics.
2. Description of the Related Art
Memories have been widely used in various electronic products. Due to the increasing need of data storage, the demands of the capacities and performances of the memories become higher and higher. Among various memory elements, resistive random access memories (RRAMs) have an extremely low operating voltage, an extremely high read/write speed, and high miniaturization of the element size and, thus, may replace the conventional flash memories and dynamic random access memories (DRAMs) as the main stream of memory elements of the next generation.
FIG. 1 shows the configuration of a conventional resistive random access memory. The conventional resistive random access memory includes a lower electrode 91 (such as platinum, Pt), a first medium 92 (with the K value of 3.9, for example), a second medium 93 (with the K value of 25, for example) and an upper electrode 94 (such as Pt). The first medium 92 is arranged on the lower electrode 91 and forms a through hole 921. The second medium 93 is partially arranged in the through hole 921. In other words, a part of the second medium 93 is arranged on the lower electrode 91 (inside the through hole 921), and another part of the second medium 93 is arranged on the first medium 92 (outside the through hole 921). The second medium 93 includes an inner periphery forming a concave portion 931. The upper electrode 94 extends from the inner periphery of the second medium 93 and defines a hole 941. In this arrangement, the first medium 92 usually has a dielectric constant (K value) much smaller than that of the second medium 93. Thus, the second medium 93 can be switched between a low resistance state (LRS) and a high resistance state (HRS). Such a resistive random access memory may be seen in an academic paper entitled “Characteristics and Mechanism of Silicon-Oxide-Based Resistance Random Access Memory” as published in IEEE ELECTRON DEVICE LETTERS, VOL. 34, No 3 on March 2013.
Nowadays, the size of the memory must be reduced due to the miniaturization of the modern electronic devices. However, reduction in volume of the memory results in the reduced size of the through hole 921. In this regard, assume the size of the through hole 921 is reduced from 4.0 μm to 0.4 μm as illustrated in FIG. 2, the forming voltage of the memory will increase from 9 to 12 volts. Namely, the forming voltage of the memory increases as the volume of the memory reduces, leading to an unstable forming voltage. In this regard, when the memory is integrated into an integrated circuit (IC), adverse effects such as high power consumption may occur if the forming voltage is too high.
In light of this, it is necessary to improve the conventional resistive random access memory.